The Spray-Mate II's GPS speed sensor functions very well and is much simpler to set up than magnetic or radar sensors. GPS sensors are more reliable than radar sensors, which have trouble sensing speed on rough terrain or in vegetation. The GPS sensor also eliminates concerns that magnetic sensors might fail to record the true speed of the ATV, particularly if the wheels slip and the ATV doesn't move as far as the sensors indicate. Speed calibration numbers supplied by the manufacturer were accurate to within 1.5 feet in 1,000 feet of travel.

The Astro II GPS (figure 6) takes about 5 minutes to acquire a satellite fix in a new location. Small LED lights indicate power to the unit and the status of the GPS signal. The GPS has not been tested under a dense forest canopy. Micro-Trak offers a more powerful GPS receiver, the Astro 5.

Figure 6—The Astro II GPS sends a signal to the control system console
as it traces the speed of the ATV. LED lights indicate power to the unit
and the status of the GPS signal.